Optical system for integrated circuit fabrication

Abstract

An optical system for integrated circuit fabrication comprises optical members made of synthetic quartz glass and fluorite, wherein: an optical member disposed in a position through which laser light is transmitted at a high light energy density, is made of single crystal fluorite; and an optical member in a position through which laser light is transmitted at a low light energy density, is made of synthetic quartz glass containing approximately such a hydrogen molecule concentration as can be doped under atmospheric pressure.

What is claimed is:  
     
       1. Optical system for integrated circuit fabrication, in which an integrated circuit pattern image is projected on a wafer using an excimer laser emitting ultraviolet light of a short wavelenght, comprising at least one crystalline optical member made of a single crystal fluorite and at least one amorphous optical member made of synthetic quartz glass, wherein said crystalline optical member is disposed in a first position closest to an exposing surface of a wafer and/or a pupil plane, which is position through which the laser light is transmitted at a relatively high light energy density ε (mJ/cm 2 ) in a range of about 0.4≦ε≦1.5 mJ/cm 2 , and said amorphous optical member is disposed in a second position remote from the exposing surface of a wafer and/or the pupil plane, which is position through which the laser light is transmitted at a relatively low light energy density ε (mJ/cm 2 ) in a range of about 0.1≦ε≦0.4 mJ/cm 2  whereby the amorphous optical member is made of quartz glass having a hydrogen molecule concentration in the range of 1×10 17  molecules/cm 3  to 5×10 18  molecules/cm 3 . 
     
     
       2. Optical system according to  claim 1 , wherein after irradiation with a pulsed laser light having a wavelength of 193 nm at an energy density per pulse of 50 mJ/cm 2  and at a pulse count of 1×10 6  the crystalline optical member has an internal transmittance of 98%/cm or more. 
     
     
       3. Optical system according to  claim 2 , wherein the birefringence of the amorphous optical member is lower than the birefringence of the crystalline optical member. 
     
     
       4. Optical system according to  claim 2 , wherein the crystalline optical member is made from a single crystal fluorite which has a homogeneity of refractive index Δn of 3×10 −6 /cm or less and a birefringence of 2 nm/cm or less, and the amorphous optical member is made from a synthetic quartz glass which has a homogeneity of refractive index Δn of 2×10 −6 /cm or less and a birefringence of 1 nm/cm or less. 
     
     
       5. Optical system according to  claim 2 , wherein the excimer laser is an ArF excimer laser emitting laser light having an oscillating wavelength width of 1.5 pm or less. 
     
     
       6. Optical system according to  claim 1 , wherein the birefringence of the amorphous optical member is lower than the birefringence of the crystalline optical member. 
     
     
       7. Optical system according to  claim 6 , wherein the crystalline optical member is made from a single crystal fluorite which has a homogeneity of refractive index Δn of 3×10 −6 /cm or less and a birefringence of 2 nm/cm or less, and the amorphous optical member is made from a synthetic quartz glass which has a homogeneity of refractive index Δn of 2×10 −6 /cm or less and a birefringence of 1 nm/cm or less. 
     
     
       8. Optical system according to  claim 6 , wherein the excimer laser is an ArF excimer laser emitting laser light having an oscillating wavelength width of 1.5 pm or less. 
     
     
       9. Optical system according to  claim 1 , wherein the crystalline optical member is made from a single crystal fluorite which has a homogeneity of refractive index Δn of 3×10 −6 /cm or less and a birefringence of 2 nm/cm or less, and the amorphous optical member is made from a synthetic quartz glass which has a homogeneity of refractive index Δn of 2×10 −6 /cm or less and a birefringence of 1 nm/cm or less. 
     
     
       10. Optical system according to  claim 9 , wherein it uses refractive optics comprising several amorphous optical members made of at least a first and a second quality of synthetic quartz glass, whereby the first quality has a hydrogen molecule concentration of at least 5×10 17  molecules/cm 3 , and the second quality has a hydrogen molecule concentration of at least 1×10 17  molecules/cm 3 . 
     
     
       11. Optical system according to the  claim 10 , wherein for the ArF excimer laser light having a wavelength of 193 nm the average transmittance of the optical system as a whole is about 98.0%/cm or more, the transmittance of the at least one amorphous optical member is 99.5%/cm or more and the transmittance for the crystalline optical member is 99.8%/cm or more, whereby at least one amorphous optical member belonging to the second quality is disposed in a region through which the laser light is transmitted at an energy density of ε≦0.1 mJ/cm 2 , and at least one amorphous optical member belonging to the first quality is disposed in a region, through which the laser light is transmitted at an energy density of 0.1<ε<0.4 mJ/cm 2 , and the at least one crystalline optical member is disposed in a region, through which the laser light is transmitted at an energy density of ε≧0.4 mJ/cm 2 . 
     
     
       12. Optical system according to  claim 11 , wherein the optical system comprises an overall optical path length composed of total optical path lengths of the at least one crystalline optical member and of the at least one amorphous optical member, wherein the total optical path length of the at least one crystalline optical member is set at 25% or less of the overall optical path length and the total optical path length of the at least one amorphous optical member belonging to the second quality is set at 50% or more of the total optical path length. 
     
     
       13. Optical system according to  claim 12 , wherein the average variation of refractive index Δn of the optical system is set at a value of Δn≦2.0×10 −6 /cm. 
     
     
       14. Optical system according to  claim 9 , wherein the excimer laser is an ArF excimer laser emitting laser light having an oscillating wavelength width of 1.5 pm or less. 
     
     
       15. Optical system according to  claim 10 , wherein the excimer laser is an ArF excimer laser emitting laser light having an oscillating wavelength width of 1.5 pm or less. 
     
     
       16. Optical system according to  claim 1 , wherein the excimer laser is an ArF excimer laser emitting laser light having an oscillating wavelength width of 1.5 pm or less. 
     
     
       17. Optical system according to  claim 16 , wherein for the ArF excimer laser light having a wavelength of 193 nm the average transmittance of the optical system as a whole is about 98.0%/cm or more, the transmittance of the at least one amorphous optical member is 99.5%/cm or more and the transmittance for the crystalline optical member is 99.8%/cm or more, whereby at least one amorphous optical member belonging to the second quality is disposed in a region through which the laser light is transmitted at an energy density of ε≦0.1 mJ/cm 2 , and at least one amorphous optical member belonging to the first quality is disposed in a region, through which the laser light is transmitted at an energy density of 0.1<ε<0.4 mJ/cm 2 , and the at least one crystalline optical member is disposed in a region, through which the laser light is transmitted at an energy density of ε≧0.4 mJ/cm 2 .